Airplane fuselages normally comprise a skin, of which the outer surface forms the aerodynamic surface of the airplane. On the inner surface it is normally provided with a plurality of stiffeners. These can be transverse stiffeners, in particular frames forming the barrel of the fuselage (either complete frames or frames that are interrupted, for example by the landing gear), or longitudinal stiffeners, such as stringers or longerons, or also other ribs.
The stiffeners thus have a curvature matching the shape of the skin and can be formed from a plurality of stiffener lengths assembled end-to-end. They are intended to provide the fuselage with an increased mechanical strength, which is reinforced by the presence of longitudinal stringers fixed to the skin and to the stiffeners, these stringers also being obtainable by assembly of lengths end-to-end. Such a fuselage is known for example from document FR 2 920 743 A1.
The stiffeners in question here have a flange intended to be fixed to the fuselage skin, and also a heel connected to the flange by a web. They can be formed by different techniques, such as the folding and the shaping of a sheet, the machining of a thick plate, or also the shaping of a profile obtained by spinning. Although these solutions are satisfactory, the ever-increasing certification requirements result in a need to find solutions that reinforce the mechanical strength of these stiffeners whilst controlling the costs.